The blog for those involved in managing windows servers , Specially for small to medium business

Monday, October 18, 2010

Network router discovery in SBS 2008 , how Connect to internet wizard works in the background

There is a brand new SBS 2008 you are setting up. You need to run a few handy wizards from the SBS console. You will encounter “The connect to internet” wizard . I will try to highlight the major processes that happen in the background.

Before starting with that, the connect to internet wizard is a by-product of Microsoft decision to segregate the ICW (internet connection wizard) of the SBS 2003 fame into multiple singular wizards.

Once you launch the wizard and click next

1. It checks the number of network cards on the system.

2. It will then check for the networks available.

A) If the DHCP Server service on the router is turned on, Windows SBS 2008 does the following:

Uses the DHCP server subnet settings on the router to set up the DHCP Server service on Windows SBS 2008. The DHCP Server service is configured to hand out Class C addresses by default on the same network as the router, from .1 to .254.IP addresses from .1 to .10 are reserved for routers, servers, printers etc.

Throws up a warning that a DHCP server exists on the router and that the network will be configured so that DHCP on the SBS 2008 is authoritative.

It will give three options

> Manage Router – load the page of the router. make the necessary changes.

> Postpone – Run the wizard another time.

> Continue – this will check the network again for DHCP servers.Choose this option if you have disabled the service on the router.

B) If the DHCP Server service on the router is turned off , Windows SBS 2008 does the following

Server multicasts a ICMP Router Discovery Message on the multicast address 224.0.0.2. This is in accordance with RFP 1256 protocol. Routers that are RFC1256 compliant will respond to this request. The Router Solicitation can be sent to the all-routers IP multicast address, 224.0.0.2, which is the local IP broadcast address that IPv4 reserved. IPv4 multicast addresses in the range 224.0.0.0/24 (from 224.0.0.0 to 224.0.0.255) are reserved for the local subnet.

Server uses the Simple Service Discovery Protocol (SSDP) Discovery Service to find routers that do not support RFC 1256.UPnP compliant devices advertise their presence in the local network via SSDP. The information sharing during this process is limited to basic information about the devices and their services, probably a UNC path , which can be used to gather more information.

Once a device is found , the server will ping the device to check if it responds .

Attempts to connect to the Internet through the device by making a DNS request to the root DNS server. Server sends 3 requests to 3 randomly chosen DNS root hint servers trying to resolve a public URL.

If the DNS Server has forwarders already configured, we will use the forwarders to do the DNS query instead of the Root Hints.

If a router is not discovered,it will prompt the user for the routers IP address. If the router is discovered, but the internet is not, wizard gives an opportunity to configure and test internet connection.If a router is found and we can connect to the internet , a finish page will be displayed.

IPv6 router

If you disable DHCP service on a IPv6 router , stateless auto-configuration is enabled . SBS will configure the DHCP service with it’s own site local IP address and make all the configuration for you.